An accurate clock generator is very important for signal-conditioning in a variety of applications. An application specific integrated circuit (ASIC) operating that utilizes such a generator in an environment is subject to substantial variations in temperature. One example of such an environment is an automotive application, in which the temperature range could be from −50 C to 150 C. An unstable clock frequency reduces the performance of the internal circuits, especially the switched-cap circuits, baud rate generator and handshake circuits.
To provide a stable reference clock, many oscillator circuits have been studied. A common one is the crystal oscillator, an example of which is disclosed, for example in U.S. Pat. No. 6,377,130. However, a crystal cannot be integrated into a single chip and its usage is limited by its size.
RC oscillators have been studied for a long time. Conventional RC oscillators are limited to low-frequency, low-precision applications sources such as tone generators, alarms or flashing indicators. Also, the temperature coefficient (TC) parameters of those resistors and capacitors are hard to control.
Many other RC circuits, like canonic RC-active frequency oscillator, require an operational amplifier as disclosed, for example in U.S. Pat. No. 5,870,345 or a comparator as disclosed in US Patent Publication No. 2005/0134393, to stabilize the oscillating frequency. To provide whether to build a high gain operational amplifier or a high speed comparator is complicated and expensive in the hardware and power consumption. This is particularly true if the frequency of the application is up to megahertz range. Also the offset voltage of the operational amplifier and comparator is temperature dependent, which gives a temperature dependent clock signal. To correct this offset, a complicated circuitry is required.
Due to the aforementioned drawbacks, conventional approaches cannot provide a stabilized oscillator circuit integrated into ASIC with a high performance. Therefore a new approach is necessary. The present invention addresses such a need.